Method of treating subterranean formation with a composition of improved viscosity control

ABSTRACT

An aqueous composition is provided which can be employed as a fracturing fluid, to suspend particulate solids or the like. The composition can be formulated to have a certain initial viscosity value which will decrease after a certain period of time to a value below the initial viscosity value. The composition comprises, water, a water soluble organic polymer as a viscosity increasing agent and as a breaker a hydrazine or hydroxylamine compound or a mixture of such compounds.

XR 3 a 8 l 8 99 1 United States Patent 1191 Nimerick 1 June 25, 1974 METHOD OF TREATING SUBTERRANEAN 3,167,510 1/1965 Alter 252/855 FORMATION WITH A COMPOSITION OF 3,302,717 2/1967 West et a1 166/283 3,310,112 3/1967 Nielsen et a1. 166/283 X IMPROVED VISCOSITY CONTROL 3,405,062 /1968 Kuhn 252/855 [75] Inventor; Kenneth H. Nimerick, Tulsa, Okla, 3,442,803 5/1969 Hoover et a1. 252/855 [73] Assignee: The Dow Chemical Company,

Mid1and, Mich. Primary ExaminerStephen J. Novosad I [22] Filed: Aug. 27, 1973 Attorney, Agent, or Firm-Bruce M. Kanuck [21] Appl. No.: 391,719

Related U.S. Application Data .[57] ABSTRACT Division 0f 9- 9 May 1971 An aqueous composition is provided which can be em- 3'7791914 wh'ch a of ployed as a fracturing fluid, to suspend particulate so]- Sept 1967 abandoned ids or the like. The composition can be formulated to have a certain initial viscosity value which will de- [52] 1.1.5.31. l66/28E32,11b63g3/(2)2 crease after a Certain period of time to a value below [28] Fr tid 308 305 R the initial viscosity value. The composition comprises, 1 0 /8 5 R water, a water soluble organic polymer as a viscosity increasing agent and as a breaker a hydrazine or hy- References Cited ggofilyggmme compound or a mlxture of such com- UNITED STATES PATENTS 3,024,191 3/1962 Jones 166/283 10 Claims, 3 Drawing Figures pazgmer 00/5 8 m g Q i) b g -O\ 4. Q O Po/ymer +/ga/ of 0 Q 85 7a A/ H Q 2 4 o 2 O- N O.\ Q po/gmer 7* ga/ of v 3i 17 0 a I O 1-1111111L 1 111111 1 1 1| 77/726 /7 had/'6 METHOD OF TREATING SUBTERRANEAN FORMATION WITH A COMPOSITION OF IMPROVED VISCOSITY CONTROL CROSS-REFERENCE TO RELATED APPLICATION This is a division of application Ser. NO. 145,495, filed May 20, 1971, now U.S. Pat. No. 3,779,914, which in turn was a continuation-impart of application Ser. No. 666,853, filed Sept. 11, 1967, now abandoned.

BACKGROUND OF THE INVENTION Fluids exhibit a measurable property known as viscosity, a term which may be broadly defined as the internal friction or molecular attraction of a given material which manifests itself in resistance to flow. It is measured in liquids by standard test procedures and is usually expressed in poises or centipoises at a specified temperature, although in oil technology it is sometimes expressed in seconds required for a given volume to flow through a specified orifice at a definite temperature. The viscosity of a liquid is an indication of a number of behavior patterns of the liquid at a given temperature including pumping characteristics, rate of flow, wetting properties, and a tendency or capacity to suspend an insoluble particulated material therein.

The invention is concerned with intentionally and desirably having the viscosity of a liquid so that it may at one time possess a high viscosity value, e.g. high capacity for suspending particulate materials, and at a subsequent time have a reduced viscosity value, e.g. lower capacity for suspending such materials. There are a number of industrial operations wherein it is desirable that the capacity of a liquid to suspend and later to drop out or permit settling of a particulate material suspended therein be controlled.

A particular need for such control exists in the 'practice of fracturing subterranean formations. A fracturing fluid (usually a liquid, although some gas may .be present), having granular insoluble particulate material suspended or slurried therein, is injected down a well penetrating the formation and forced back into the formation (employing the height of the hydraulic head of the liquid to provide pressure and hence commonly known as hydraulic fracturing). Through the instrumentality of such operation, the formation is caused to crack or fracture thereby eflectuating improved communication between a fluid (e.g. oil, gas, water, etc.) in the formation and the well. Fracturing is customarily conducted by employing oil, water, (sometimes in a thickened or gelled state) or an emulsion thereof which has suspended therein particles which are substantially insoluble in the liquid and the fluids of the formation, at least a portion of the particles thereby being forced to lodge in the fractures created, thus propping open the fractures when the fracturing pressures are subsequently released and the well put back in production.

To maintain a propping agent suspended in a liquid until it is lodged in a fracture presents problems since the propping agent tends to settle out as the rate of movement of the liquid. after leaving the wellbore, slackens. This sometimes occurs prematurely resulting in depositing the propping agent in the wellbore or immediately adjacent to the wellbore, causing what is known as a sand-out or a screen-out. In efforts to avoid the premature deposition of the propping agent, liquids have been used, the suspending ability of which is improved by thickening the same with a suspending agent (a viscosity increasing agent). This approach to the problem, though aiding in maintaining the propping agent in suspension for an additional time, introduces the added problem of tending to prevent the propping agent from lodging securely in the newly created'fractures and to prevent the removal of the fracturing liquid from the fractures.

The use of breakers to reduce the viscosity of certain selected viscous water soluble organic polymeric aqueous solutions is not new. In U.S. Pat. No. 2,483,936 the viscosity of an aqueous solution of guar gum is reduced by dispersing in the solution sodium and hydrogen peroxide. In U.S. Pat. No. 3,024,191 it is asserted that the viscosity of an aqueous solution thickened with carboxymethyl cellulose can only be effectively reduced with a perborate. Further, in U.S. Pat. No. 3,167,5l0 the viscosity of aqueous solutions thickened with guar gum can be decreased by employing a persulfate if the solution is maintained at a temperature of at least F. In U.S. Pat. No. 3,442,803 a specific polymer of acrylamide and methylenebisacrylamide is employed to increase the viscosity of aqueous solutions. The viscous solution can be broken, i.e. the viscosity decreased, by adding a water soluble persulfate or perborate thereto. However, in all of these patents a specific breaker was found to be ef fective only on a specific water soluble organic polymeric viscosity increasing agent, and in U.S. Pat. No. 3,167,510 only at an elevated temperature. In the present invention a class of breakers have been discovered which are effective to break an aqueous solution containing one or more of a broad class of water soluble organic polymeric viscosity increasing agents.

A need clearly exists for a liquid which has an initial relatively high suspending ability, e.g. high viscosity, during injection and fracturing and thereafter within a relatively short time, autonomously converts to a liquid of relatively low suspending ability to drop out the particles and facilitate its removal from the fractures. There is also a need for plugging and diverting compositions which serve as a temporarily fluid loss agent, e.g. in thief zones, and thereafter break to a low viscosity for easy removal.

SUMMARY OF THE INVENTION The invention is a novel composition of matter and use thereof. The composition comprises a viscous mixture of a water soluble organic polymer and water, with which is admixed an effective quantity of a compound selected from the group consisting of a water soluble hydroxylamine, hydrazine. compound or mixtures thereof to decrease the viscosity of the composition after a certain period of time.

IN THE DRAWINGS FIGS. 1, 2 and 3 illustrate certain data generated in working Examples 1, 2 and 3.

Hydrazine and hydroxylamine compounds can include any of those compounds which are sufficiently water soluble to be effective in the practice of the present invention.

Hydrazine compounds include hydrazine and water soluble hydrazine derivatives such as substituted hydrazine wherein one or more of the hydrogen atoms is replaced by, for example, an organic group, e.g. an alkyl or aromatic hydrocarbon, a metal ion; hydrazine salts such as those formed with mono basic acids, e.g. HCl and dibasic acids such as H 50 carboxylic acids and the like. Several well-known analytical methods can be employed to determine whether a certain compound in fact forms hydrazinium ions in solution. See specifically those methods taught at pp. 184 and 185 of The Encyclopedia of Chemical Technology, Vol. 11, 1966, 2nd Ed., said teachings being specifically incorporated herein by reference. Specific hydrazine compounds which can be employed include, for example, hydrazine monochloride, hydrazine dihydrochloride, dihydrazine disulfate, monohydrazine sulfate, hydrazine disulfate, stearic dihydrazide, succinyl dihydrazide, adipic dihydrazide, copper dihydrazinium sulfate, hydrazinium dihydrobromide, dihydrazine oxalate, hydrazinium acid adipate, zinc dihydrazine sulfate, zinc dihydrazine chloride, cobalt dihydrazine chloride, sebacic dihydrazide, zinc dithiocarbazinate, carbohydrazide, dihydrazine acid phosphate, hydrazine borate, copper hydrazinium phosphate-copper sulfate complex, copper sulfate-hydrazine bromide complex, copper sulfatehydrazine oxalate complex, thiosemicarbazide, hydrazine adipic acid acetone complex, cinnamalazine, glyoxal-di-para-nitrophenyl hydrazine, 2,4-dinitrophenyl-hydrazine acetate, benzalazine, 2,4- dichlorobenzalazine, a-naphthalazine,hydrazinium nbutyl phosphate, hydrazinium methyl phosphate, hydrazinium isopropyl phosphate. tetra-hydrazinium pyrophosphate, monohydrazine phosphate, dihydrazinium phosphate, monohydrazinium dihypophosphite, N,N-diphenyl carbamyl hydrazide, monomethylhydrazine sulfate, 2,4-dichloro-6-(ochloroaniline)-s-triazine, dihydrazine tartrate, zinc dimethylhydrazine chloride.

The other suitable breaker is a hydroxylamine compound which includes hydroxylamine and water soluble hydroxylamine derivatives such as, for example, ammonium-type salts formed with inorganic acids, e.g. those disclosed at page 494, Table 2 of The Encyclopedia of Chemical Technology, Vol. 11, 1966, 2nd Ed., and coordination complexes with metal ions such as disclosed at p. 494, Table 3 of the same Encyclopedia, said teachings being specifically incorporated herein by reference. The compounds listed in these aforementioned Tables 2 and 3 are:

Table 2 Hydroxylammonium Salts Salt Formula chloride (NH OHJCI sulfate (NH ,OH),SO, acid sulfate (NH OH )HSO,

' phosphate (NH OHHPO,

arsenate (NH OH) AsO sulfamate (NH OH)SO NH, perchlorate (NH;,OH)C10, iodide (NH OH)I fluorosilicate (NH OH),SiF .1H,O chlorostannate (NH,-,OH),SnCl aluminum sulfate (NH ,OH)A1(SO,),'12H,O ferric sulfate (NH,OH)Fc(SO,),-l 2H,O

chromium sulfate magnesium sulfate uranatc ethyl sulfate Table 3 Hydroxylamine Complex Salts In general, any hydroxylamine compound which is sufficiently soluble in water to be effective as a breaker in the practice of the present invention is suitable.

Methods of preparation, properties of specific hydroxylamine and hydrazine compounds and other useful information can be found at pages 164-196 and 493-508 of The Encyclopedia of Chemical Technology, Vol. 1 1, 1966, 2nd Ed, said teachings are specifically incorporated herein by reference.

Any polymer which is water-dispersible and forms a pumpable gel or otherwise viscous system having suspending properties in water may be employed in the practice of the invention. Such polymers include (1) acrylamide polymers which may be linear polyacrylamide, acrylamide polymers cross-linked with a limited amount of a cross-linking agent, and acrylamide'copolymers prepared by copolymerizing acrylamide with a minor proportion of a monomer copolymerizable therewith, e.g. vinylbenzylsulfonate or vinylbenzenesulfonate; (2) polyvinylpyrrolidone; (3) polyvinylmorpholinone; (4) cellulosic polymers and derivatives thereof; (5) natural gums such as guar, tragacanth, lrish moss, soy bean, and modified starches, e.g. those disclosed in Davidison-Sittig, Water Soluble Resins, pp. 13-49, 2nd Ed. (1962); and (6) water-soluble alkaline metal salts of suchpolymers, copolymers, and gums. For simplicityof expression all such polymeric additaments will be referred to herein merely as polymers.

The polymers degraded by the process of the invention are water-soluble or water-dispersible, resinous,

high molecular weight, organic polymers, sometimes referred to as hydrophilic polymeric colloids. The term water-soluble'as employed in the foregoing technology, means dispersible in water to provide a visually homogeneous system. Such polymers are usually essentially linear or branched in structure, but may be to some extent cross-linked so long as the polymer is effectively swollen by and uniformly dispersed in water.

, Water-solubility is imparted to such polymers by incorporating in' and along the polymer chain a number of hydrophilic moieties sufficient to more than offset the otherwise hydrophobic character of the organic polymer. One class of such hydrophilic moieties includes the ionizable groups. Among these are the sulfate and sulfonate acid and salt groups, carboxylate salt groups, amine and ammonium groups (the latter being inclusive of protonated forms of amines as well as quaternary derivatives of the amines, e.g. mono-, diand trialkyl substituted ammonium salt groups), and phosphonic acid and monoand dibasic salts thereof. Whenever acid salts are referred to, those preferred are the alkali metal, alkaline earth metal (water-soluble species thereof), and ammonium salts. The total carbons of any substituents on the nitrogen in the ammonium cations should not exceed about 12 carbons in order to insure the water-solubility of the resulting salt. Another class of hydrophilic moieties are such nonionizable groups as carboxamide, and monoand dialkyl nitro gen-substituted carboxamides, having a total of up to the like, in and along the polymer chain, in a sufiicient amount to render the resulting polymer water-soluble, as defined above.

Resinous, as employed to characterize the polymers, means macromolecular in size. It is otherwise apropos to characterize such polymers as being of high molecular weight. While a given minimum molecular weight would be arbitrary, especially when used to define broadly the transition point between low polymers and macromolecules, polymers are to be generally considered as having high molecular weights or being resinous for purposes herein at average molecular weights above about 100,000. in the instance of vinyl addition polymers, the resinous polymers may attain average molecular weights as great as million or more.

-Water-soluble resinous polymers are obtained as naturally occurring polymers or by various modifications of the naturally occurring polymers as well asby synthesis by means of addition or condensation polymerizations of appropriate monomers. Technology for preparing water-soluble polymers useful herein is known. The chemistry of many water-soluble resinous polymers applicable for use in the process of the invention will be found among the teachings concerning additional polymers obtained by ethylenic polymerization such as those described in Hedrick et al,-US. Pat. No. 2,625,529; Aimone et al, US. Pat. No. 2,740,522; and Booth et al, U.S. Pat. No. 2,729,557. A variety of polysaccharide derivatives are described by Gloor in US. Pat. No. 2,728,725. Polyurethanes and chain extended polyols will be found in Honea et al, US. Pat. No. 3,054,778 and Colwell et al, U.S.. Pat. No. 3,020,231, respectively, and a variety of polycarbamates and lactams in Hibbard et al, US. Pat. No. 3,044,992; Walles et al, US. Pat. No. 2,946,772; Vitales, U.S. Pat. No. 2,874,124; and Fong et al, US. Pat. .No. 3,000,830. These are to mention but a few of the well-known chemical preparations for water-soluble macromolecules or resinous polymers. The polymers concerned herein will often be otherwise identified as watersoluble organic polyelectrolytes. Further, general descriptions of a variety of water-soluble resinous polymers are contained in Davidson and Sittig, Water-Soluble Resins, Reinhold-Publishing Corp., New York, 1962.

Polyacrylamides are commonly prepared by admixing, with an aqueous solution of acrylamide monomer, at substantially a neutral pH value a redox type catalyst, e.g. a persulfate of peroxide, in an amount of between about 100 and 700 parts thereof per million parts of monomer, and subjecting the resulting solution to a temperature between about 20C and. about 60C for from about l to about 5 hours during which the acrylamide polymerizes to a polymer having an average molecular weight of at least about 100,000, e.g. from about 1,000,000 to 2,000,000. The polymer so made is then separated, by known techniques, e.g. evaporation, from the reaction medium and dried and particulated. Acrylamide polymers prepared in this manner have a low extent of hydrolysis and may be referred to hereinafter as Polymer A. Hydrolysis as applied to such polymers means that carboxamide groups are converted to carboxylic groups.

Polyacrylamide polymers almost invariably are hydrolyzed to some extent. A high degree of hydrolysis is sometimes desirable. The extent of hydrolysis can be 6 increased by raising the pH value of the mixture during polymerization, e.g. by addition of NaOh. Acrylamide polymers which have a relatively higher per cent hydrolyzed carboxamide group may be referred to herein as Polymer B.

Details on acrylamide polymers may be obtained from the literature, e.g. US. Pat. No. 2,820,777 and a publication entitled Separan, Forms No. -28- 460,62 and -65 published by The Dow Chemical Company, Midland, Mich.

Cellulose ethers are prepared by first reacting alkali cellulose, in any order, with suitable amounts of a halogenated lower carboxylic acid and a hydroxyalkylating reagent or alkyl halide. By alkali cellulose is meant the reaction product of cellulose and an alkali metal hydroxide or quaternary ammonium base. Specific examples are sodium hydroxide, potassium hydroxide, and trimethyl benzyl ammonium hydroxide. Useful lower acids include monochloroacetic acid, monochloropropionic acid, and alkali metal salts of the foregoing acids. Suitable hydroxyalkylating agents include the lower alkylene oxides such as ethyleneand propylene oxides. Such oxides can be formed in situ by reaction of the appropriate chlorohydrins with an alkali hydroxide.

The alkali cellulose may be prepared prior to the etherification reaction, or prepared in situ by incorporating cellulose and alkali hydroxide into the reaction system along with one or more of the etherifying reagents. Reaction techniques of this nature are taught in US. Pat. Nos. 2,469,764 and 2,510,355. 'If desired,

however, etherification of the alkalized cellulose can be carried out in the presence of an inert diluent, which promotes uniform distribution of the reactants, a condition otherwise obtained by vigorous stirring of the reaction system. lllustrating such a technique are US. Pat. Nos. 2,067,946; 2,517,577; 2,572,037; 2,839,526; and 3,131,176.

Cellulose fibers suitable for preparing the ethers of the invention include any appropriate cellulose raw materials such as cotton or wood pulp of a type convenvtionally used for etherification reactions. Such cellulose material may be used in any physical form such as vided or flocked cellulose fibers or ground cellulose fibers. Cotton linters are preferred. 1

A mixed carboxymethylhydroxyalkyl cellulose ether may be prepared according to a stagewise mass reaction technique. A cellulose fiber stock suitable for the preparation of cellulose ethers is incorporated into a reactor equipped with means for inducing severe agitation of the reaction mass. Cotton linters are a good starting material for this reaction but ground wood cellulose may also be used to advantage. Illustratively, suitable mixing is accomplished by introducing rotary as well as beating motion into the reaction mass. This is accomplished with counterrotating turbines and double helical agitators. Along with the cellulose, is incorporated an alkali hydroxide such as sodium hydroxide or potassium hydroxide of a quaternary ammonium compound. Usually the base is in an aqueous solution as concentrated as is convenient for spraying it onto the cellulose fibers. At this point, if it has not already been done, the reactor is evacuated by removing oxygen.

. Thereafter, the carboxyalkylating reagent (e.g. chloroacetic acid) is incorporated'into the alkalized reaction mass in an amount sufficient to provide a carboxyalkyl M.S. of from about 0.05 to about 0.2. The hydroxyalkylating reagent is then introduced in an amount sufficient to produce a hydroxyalkyl substitution of at least from about 1.5 to as much as about 5. The carboxyalkylating reagent is again added in an amount sufficient to produce a product with a total carboxyalkyl M.S. in the range of from about 0.2 to about 1.2. The additions of the etherifying reagents are accomplished at reactor temperatures within the range of from about 30C to about 80C.

The reaction mass is then dried as a basic product at a temperature below about 140F to a residual moisture content of less than about 25 per cent, preferably to less than about 16 per cent, by weight of the reaction mass. The dried product may then be ground, if a finer particulate state is desired.

It is, therefore, seen that methods of preparing the polymers useful in the practice of the invention are well-known.

The exact amount of the viscosity increasing or suspending agent employed will depend on the desired initial viscosity of the aqueoussolution. The desired viscosity depends in turn on the particular use of the composition. Simple laboratory procedures can be employed to establish the amount of any particular viscosity increasingagent required to give a desired viscosity. Temperature can effect the viscosity and should be taken into consideration in determining the effectiveness of the viscosity increasing agent.

The amount of breaker employed will determine, at the temperature of use of the composition, the time re quired to decrease the viscosity of the composition to a certain value. Again simple laboratory tests should be conducted to establish the amount of breaker required to decrease the viscosity of a specific composition to a certain value, within a certain period of time, at a certain temperature. It has been found that the breakers of the present invention are generally more active at higher temperatures. Therefore, as a general rule, a lesser amount of the breaker is required when the composition is to be subjected to higher temperature.

The following examples illustrate the practice of-the present invention and further show simple laboratory procedures which can be employed .to design specific compositions to have characteristics, i.e. initial viscosity at a certain temperature, amount of breaker required to decrease the viscosity of the composition to a certain value within a certain period of time, and the like.

In U.S. Pat. No. 3,024,191 (discussed earlier) certain curves were established to show amounts of sodium perborate which should be used if a viscosity of at least 30 centipoise is to be retained for l, 2 or 3 hours, at any specified temperature. A viscosity of 30 centipoise was chosen since it was determined that a dispersion of CMC more viscous than this was required to support large propping agents. The amount of viscosity increasing agent required to provide a composition which will support a particular size particle will depend on the exact agent employed. However, this can be easily established for any desired agent. Likewise, curves such as disclosed in U.S. Pat. No. 3,024,191 can be established for any particular combination of breaker and viscosity increasing agent within the scope of the present invention. This is helpful in selecting the required amount of breaker required to be employed in any specific situation.

Generally, in the practice of the invention, a small but effective concentration of the polymer e g one which results in an initial viscosity of the aqueous dispersion at the temperature concerned, of not less than about 10, and not appreciably greater than about 5,000 centipoises is used. This viscosity is determined by using a Fann viscosimeter at a temperature of 25C at rpm. Specific situations may require higher or lower viscosity requirements. Operable concentrations will depend on the particular polymer employed and in general ranges from less than about 0.1 to about 2.0, or greater, per cent by weight of the aqueous composition. For practical purposes, the amount employed is sometimes calculated as weight of polymer per specified volume of composition, e. g. between about 10 pounds and about pounds of polymer per 1,000 gallons of the resulting aqueous composition. Between about 20 and 50 pounds of polymer per thousand gallons of aqueous composition are usually recommended for fracturing uses.

The viscosity reducing agent required by the invention, e.g. hydrazine, hydroxylamine, etc. is usually employed in a sufficient amount to reduce the critical viscosity of the composition to a value of 15 centipoise or less within a period of no longer than about 72 hours. Generally, between about 0.03 and 20 parts by weight per I00 parts by weight of polymer present in the liquid composition is sufi'rcient depending upon polymer concentration, type of polymer and exact agent employed. The viscosity reducing agent employed according to the invention is more active at higher temperatures and, accordingly, lesser amounts are necessary at higher temperatures.

EXAMPLE I In all the examples a Fann viscosimeter at 100 rpm was employed to establish the viscosities shown.

The tests depicted in the graphs were conducted by employing an acrylamide polymer designated Polymer B above. FIGS. 1 and 2 of the drawing, annexed hereto, show graphically the effect of admixing the viscosity reducing agent with an aqueous polymer composition, as illustrated by hydrazine and by hydrogen peroxide in accordance with the invention.

The polymer so prepared was admixed with water in the amount of 60 pounds polymer per 1,000 gallons of water.

For comparative purposes, the initial viscosity of the aqueous polymer dispersion at 150F was ascertained. After about 28 hours, the viscosity was again measured.

The values were plotted on FIG. 1 as a solid line. To illustrate the practice of the invention, a gallon of 30 percent by weight hydrogen peroxide in water was added to a second 1,000-gallon portion of the aqueous polymer dispersion. Six viscosity values thereof were also ascertained at 150F over a period of 28 hours. The results are plotted on FIG. I as a heavy broken line.

A gallon of 85 percent by weight hydrazine in water was then admixed with a third 1,000-gallon portion of the aqueous polymer dispersion and six viscosity values thereof ascertained at l50F over a period of 28 hours. The results thereof are also plotted on FIG. 1 as a thin broken line.

Reference to FIG. 1 shows that the viscosity of the aqueous polymer dispersion, containing no further additive for comparative purposes, had substantially the same viscosity over the 28-hour period. In marked contrast thereto the aqueous polymer dispersion containing either the hydrazine or hydrogen peroxide showed a desirable drop in viscosity at after one-half hour which became more abrupt after about 1 hour and which continued to drop with some gradual variations so long as viscosity values were taken. Indications are, by extrapolation, that the viscosity continued to drop further with additional time until it approached that of the composition without the polymer (due to the gradual degradation of the polymer by the additament).

EXAMPLE 2 In this series of tests, polyacrylamide, prepared as described, was admixed with water in the amount of 20 pounds of polymer per 1,000 gallons of water. An initial viscosity value and a viscosity value after about 24 hours were obtained thereon. The results are plotted as a solid line in FIG. 2. To a second 1,000-gallon portion of the aqueous polymer dispersion so prepared was admixed 0.87 gallon of 85 percent by weight hydrazine in water at 80F. An initial viscosity value and values through 24 hours at 80F were obtained thereon and the results plotted as a thin broken line in FIG. 2.

A third aqueous polymer dispersion was prepared by admixing polyacrylamide in water in the amount of '40 pounds of polyacrylamide per 1,000 gallons of water. Initial and 24 hour viscosity values were obtained and recorded as a solid line in FIG. 2. A fourth aqueous polymer dispersion was prepared like the third except 1 gallon of 30 percent by weight hydrogen peroxide in water was admixed therewith. Viscosity values were obtained at 80F and the results plotted as a thin broken line in FIG. 2.

The results, as plotted on FIG. 2, show that hydrazine is highly effective as a viscosity reducing agent at 80F, effectuating significant reduction after about threefourths of an hour and more marked reduction after about 2 hours. It also shows that the viscosity, of the polymer dispersion only, as was shown in FIG. 1, also remains substantially constant in the absence of either hydrazine or hydrogen peroxide. FIG. 2 further shows that the hydrogen peroxide, in contrast to Series One (run at l50F), is relatively ineffective at 80F as a viscosity reducer.

EXAMPLE 3 In this series of tests, guar gum (also designated broadly as a polymer) was admixed with water in the amount of 60 pounds of gum per 1,000 gallons of water. An initial viscosity value was taken on the gumthickened composition, so made, and is shown in FIG.

Thereafter. four 1,000-gallon portions of the gumthickened water were selected for testing. Two 1,000- gallon portions were maintained at a temperature of 80"F and the other two- 1,000-gallon portions were heated to and maintained at l50F. With one of the portions at 80F and one of the portions at l50F were admixed two gallons of 30 percent by weight hydrogen peroxide in water. Viscosity values were taken at about 0.5 hour after the admixtures were made and again after 24 hours. Results are shown in FIG. 3 wherein the viscosity results of the two thickened water portions without viscosity reducing agent were plotted as solid 10 lines and the values of those containing the hydrogen tion provides a way of increasing the viscosity and hence the capacity to suspend particulate materials, of

an aqueous liquid by admixing with such liquid a polymer or natural gum in an amount sufficient to increase the viscosity to the desired value and the viscosity can be made to lessen within a short time by the presence of a selected viscosity reducer, according to the invention of which hydrazine is illustrative, thereby autonomously decreasing the viscosity to a desirably low value so that such liquid may be readily removed from confining spaces such as fractures in rock and underground geological formations.

Further examples-of the practice of the invention follow:

EXAMPLE 4 H 7 An a'crylamide polymer prepared according to the procedure and described above as Polymer B was admixed with water in an amount of 30 pounds of the polymer per 1,000 gallons of water. For convenience in calculation, 30 pounds of polymer per 1,000 gallons of water is about 0.36 per cent of polymer by weight. Accordingly, 5 pounds of viscosity reducer, when employed, is about 0.06 percent thereof by weight. Mixing was continued until the polymer was completely dispersed. Viscosity was measured at that time employing a Fann viscosimeter at 100 rpm, as above, and found to be 49.0.

With equal size portions of the aqueous polymer dispersion so made were then admixed the various viscostaining the additive and thereafter periodically after the lapse of the hours set out in the tables under which viscosity values appear.

TABLE I.EFFICACY OF VARIOUS VISCOSITY REDUCING AGENTS ON AQUEOUS POLYMER B DISPERSIONS AT F ACCORDING TO THEINVENTION Viscosity in centipoise after Test identification Additive used in lb/lOOO gallons of water 1 hr 2.5 hrs 4 hrs 24 hrs 48 hrs 72 hrs a None 49 49 48 48.4 1... Potassium permanganate 5. 30.0 20.0 9.6 4.0 2... Potassium permanganate l. 17.1 8.4 7.2 3... Potassium pen'odate 5 49.0 45.0 4.2 4... Potassium periodate'1....... 46.5 6.6 3.6

.. Potassium periodate 0.5 48.0 34.2 4.6

6.... Ammonium persulfate 5 41.4 40.8 39.2 13.8

7 Hydrazine sulfate 5 39.0 29.0 9.6 3.0

8 Hydrazine sulfate 1 48.0 31.5 20.0

9 I-lydrazine3. 6 45.0 43.8 36.6 v 15.6 10 Hydrogen peroxide 2 45.0 43.8 38.2 10.2

The initial viscosity of the polymer dispersion before adding the additive was 49 centipoises.

A dash indicates that no viscosity value was obtained at that time interval.

Reference to Table 1 shows the efficacy of the viscosity reducers employed in the tests, to lower viscosity autogeneously of polymer dispersions or solutions according to the invention, although practiced at the relatively low temperature of 80F. Some of the additives perform better than others, e.g. potassium permanganate, even at only 1 pound per 1,000 gallons, and potassium periodate even at only 0.5 pound per 1,000 gallons, give exceptionally good results.

In general, better results are obtained when 5 pounds of additive per 1,000 gallons are employed than when only 0.5, 1 or 2 pounds are employed.

EXAMPLE 5 The series of tests of Example 4 were repeated except varied, asset out Tab1e 111 infra that all the tests were conducted at 150F. The initial viscosity of 150F prior to addition of additive was 38.4 cps. The results are shown in Table 11.

Reference to Table II shows that the viscosity reducing agents employed in Example 5 according to the invention are even more effective at 150F than at the 80F temperature of the examples of Example 4.

EXAMPLE 6 The procedure of Examples 4 and 5 was followed in this series of tests, employing the same type of polyacrylamide polymer but'wherein the amount of polymer, the temperature, and the type and amount of viscosity reducing agent, according to the invention, were .TABLE II.EFFICACY OF VARIOUS VISCOSITY REDUCING AGENTS ON AQUEOUS POLYMER B DISPERSIONS AT 150F ACCORDING TO THE INVENTION Test identification Additive used in Ila/1000 gallons of water 1 hr 2 hrs 4 hrs 24 hrs 48 hrs None 38.4 36.9 36.6 38.0 Hydrogen peroxide, 5 27.6 22.8 12.0 Hydrazine, 5.... 21.6 14.1 3.0 Hydrazine, 1.... 1 21.3 6.9 63 Sodium peroxide. 5... 27.3 19.2 7.2 Hydrazine sulfate, 5.. 21.3 18.6 3.6 Hydrazine sulfate. 1 12.6 4.2 Ammonium persulfate, 5.. 3.9 3.0 Ammonium persulfate. 1.. 3.6 Sodium chromate. 5 29.7 29.1 9.0 Potassium iodate, 5 3.0 Potassium permanganate, 4.2 3.6 Hydroxylamine hydrochloride, 5... 27.0 24.9 3.0 Hydroxylamine hydrochloride, 1... 22.2 7.2 6.9 Sodium perborate, 1 27.0 11.1 9.6 25 Calcium hypochlorite. 5 25.8 12.9 12.0

Viscosity in centipoises after The initial viscosity before adding the additive was 38.4 cps.

A dash indicates that no viscosity value was obtained at that time interval TABLE III.-EFFICACY OF VARIOUS VISCOSITY REDUCING AGENTS ON AQUEOUS POLYMER B DISPERSIONS AT 80F OR 150F WHEREIN THE CONCENTRATION OETHE POLYMER AND THE RATIO OF VISCOSITY REDUCING AGENT (ADDITIVE) ARE VARIED Polymer Ratio of used in polymer lb/ 1000 to addi- Temper- Viscosity in cps after Test gallons of tive by ature identification water Additive in lbs/1000 gallons of water weight in F 1v hr 3 hrs 24 hrs 48 hrs None 80 '48 51 48 30 0.5 potassium periodate: 51.6 14.0 8.4 30 0.25 potassium periodate. 80 49.2 20.4 8.6 30 Olgptassipg periodate 300 80 48.0 27.0 12.0 30 5 hydrazine sulfate 6 80 39.0 9.6 30 1 hydrazine sulfate 30 80 31.5 m 20 0 30 5 ammonium persulfate. 6 80 41.4 34.2 70 None 80 l44.6 7' 140.4 140.0 130.0 70 5 potassium periodate... 14 80 114.0 103.0 12.0 4.0. 70 1 potassium periodate... 70 80 133.2 114 18.0 5.0 70 0.5 potassium periodate... 80 126.0 37.8 25.2 70 0.25 potassium periodate. 280 80 131.0 63.0 70 10 hydrazine sulfate..... 7 80 118 75.2 75.0 70 5 hydrazine sulfate 14 80 134.4 135.0 126.0 111.8 70 10 ammonium persulfate.. 7 80 122.0 T 87.6 65.0 70 5 ammonium persulfate.... 14 80 135.0 126.0 109.0 57.0 70 10 potassium bromate.. 7 80 129.0 121.0 1 17.0 70 5 potassium bromate.... 14 80 138.6 131.0 126.0 124.6 30 None 39.6 39.6 38.7 30 5 potassium periodate... 6 150 2.4 30 1 potassium periodate... 30 150 2.4 30 0.5 potassium periodate 60 150 2.4 30 0.1 potassium periodate... 300 150 22.8 8.1 6.3 30 0.05 potassium periodate. 600 150 27.6 18 0 16.2 16.0 30 0.01 potassium periodate.... 3000 150 36.3 34.2 31 2 30 0.5 ammonium persulfate... 60 150 15.6 2.4 30 0.1 ammonium persulfate... 300 150 27.9 4.2 30 0.05 ammonium persulfate.. 600 150 30.6 26 4 13.8 13 2 30 0.5 hydrazine sulfate... 60 150 28.5 3.6 30 0.1 hydrazine sulfate... 300 150 33.0 10.2 7.2 30 0.05 hydrazine sulfate 600 150 28.8 26 4 15.3 12.3

Table III-Continued TABLE III.EFFICACY OF VARIOUS VISCOSITY REDUCING AGENTS ON AQUEOUS POLYMER B DISPERSIONS AT 80F OR 150F WHEREIN THE CONCENTRATION OF THE POLYMER AND THE RATIO OF VISCOSITY REDUCING AGENT (ADDITIVE) ARE VARIED Polymer Ratio of v usedin polymer 7 lb/1000 to addi- Temper Viscosity in cps after Test gallons of tive by ature identification water Additive in lbs/1000 gallons of water weight in'F 1 hr 3 hrs 24 hrs 48 hrs 30 potassium bromate V 6 150 32.4 30.0 70 None 150 102.0 102.0 102.0 70 l potassium periodate.... 70 150 12.9 6.0 70 0.25 potassium periodate... 280 150 28.6 19.2 18.0 70 5 hydrazine sulfate 14 150 87.0 13.2 6.6 70 l hydrazine sulfate 70 150 93.0 14.7 6.9 70 0.25 hydrazine sulfate 280 150 99.0 33.3 15.9

The initial viscosity of 30 pounds of polymer per 1000 gallons water at 80F was 49.5 cps.

The initial viscosity of 70 pounds of polymer per 1000 gallons waterat 80F was 144.6 cps.

Reference to Table III shows that the oxidizing agents 5 and amine compounds therein used are effective at a ratio of polymer to viscosity reducer varying between 6 and 3,000 to lower the viscosity of aqueous polymer dispersions at both 80F and 150F. It shows that the amount of polymer may be varied between 30 and 70.

pounds per 1,000 gallons of water.

EXAMPLE 7 "The initial viscosity of 30 pounds of polymer per 1000 gallons water at 150F was 38.2 cps. The initial viscosity of 70 pounds of polymer per.1000 gallons ofwater at 150F was 99.0 cps.

Reference to the results of the tests of Example 7 shows that an acrylamide polymer prepared according to Procedure A when dispersed in water to increase the viscosity yields readily to the action of the viscosity reducers employed whereby the viscosity is markedly reduced according to the invention.

EXAMPLE 8 V.

This series of tests were conducted similarly to those of Examples 6 and 7 except that the polymer employed 30 was carboxymethylhydroxyethylcellulose in an amount of 30 pounds thereof per 1,000 gallons of water. The temperature was 80F. The type and amount of viscosity reducer employed and the resulting viscosity values, determined as above, are set out in Table V. The aver- 35 age initial viscosity before adding the additive was 21.8

cps.

TABLE lV.-EFFICACY OF VARIOUS VISCOSITY REDUCING AGENTS ON AQUEOUS POLYMER A DISPERSIONS AT 0R W WHEREIN THE ONCENT TIO F E POLYM ND AIIQQEQ9LTX8D119113 9. QENT ADDIT'IVEYI' STHRTE'D" Polymer Ratio of used in polymer lb/1000 to addi- Temper- Viscosity in cps after Test gallons of tive by ature identification water Additive used per 1000 gallons of water weight in F 1 hr 4 hrs 24 hrs 48 hrs None 80 21.3 22.5 21.9 21.0 30 0.25 potassium periodate... 120 80 20.1 19.2 16.8 6.0- 30' 0.1 potassium periodate. 300 80 21.0 20.7 20.4 20.0 70 None 80 58.8 59.1 60.0 70 2 potassium periodate. 80 51.6 49.0 29.4 20.4 30 None 150 14.7 11.1 9.8 9.8 30 0.05 potassium periodate... 600 150 15.0 13.8 8.7 7.0 30 0.1 potassium periodate.... 300 150 10.2 10 2 8.1 7.2 30 1 potassium periodate.... 30 150 2.4 30 0.05 hydrazine sulfate. 600 150 12.6 11.4 7.5 7.0 30 0.1 hydrazine sulfate... 300 150 11.4 9.6 5.7 4.2 30 0.5 hydrazine sulfate... 150 11.4 8.4 2.4 None 150 34.2 33.0 32.3 30.0

70 0.1 potassium periodate. 700- 150 29.4 27.0 22.2 17.1

70 0.5 potassium periodate. 350 150 29.4 27.0 21.9 v 16.1 70 1 potassium periodate..;.... 70 150 6.9 3.6 70 0.05 ammonium persulfate. 1400 150 31.2 25.2 14.4 13.2 70 0.1 ammonium persulfate.. 700 150 24.6 14.1 8.4 8.7 70 0.5 ammonium persulfate.. 15.3 7.5 3.0 70 1 ammonium persulfate..... 70 150 12.0 5.7 -3.0 70 0.5 hydrazine sulfate 140 150 32.1 28.8 15.0 7.8

1 Initial viscosity of 30 lbs. of polymer per 1000 gallons of water 1 at 80F was 21.6 cps.

1 Initial viscosity of 70 lbs. of polymer per 1000 gallons of water Initial viscosity of 30 lbs. of polymer per 1000 gallons of water at 150F was 14.3 cps.

Initial viscosity of 70 lbs. of polymer per 1000 gallons of water at 150F was 34.2 cps.

' 3 ,8 1 8 ,991 1 16 TABLE v. EI='EI6AcY OF VARIOUS VISCOSITY REDUCING AGENTS oN'A UEoUs DISPERSION- oEcARBoMETHYL- HYDROXYETHYL CELLULOSE AT 80F IN AMOUNT OF POUNDS PER THOUSAND GALLONS OF WATER Viscosity in cps after Test Viscosity reducer employed in lbper 1000 identification gallons of water 1 hr 2.5 hrs 4 hrs 18 hrs 24 hrs 48 hrs k None 22.2 22.2 21.0 20.8 77.. 5 sodium chlorate 21.0 20.4 19.8 18.6 78.. 5 hydroxylamide hydrochloride 19.9 19.2 14.4 9.0 79.. 5 potassium perrnangate 19.8 12.0 4.0 2.5 80.. 1 potassium permangate. 15.0 10.2 9.0 81.. 5 sodium chromate..... 21.0 20.6 18.0 15.0 82. 5 potassium periodate.. 18.0 12.0 3.6 2.0 83.. 1 potassium periodate.. 14.1 6.6 I 6.3 84.. 5 potassium bromate... 21.0 20.0 18.6 17.4 85.. 5 sodium peroxide 19.8 18.6 18.0 17.4 86.. 5 ammonium persulfate. 20.4 19.8 17.4 13.8 87.. 1 ammonium persulfate. 20.4 19.5 18.3 88.. 5 hydrazine sulfate... 19.2 19.0 14.4 6.6 89.. l hydrazine sulfate... 17.1 7.2 5.2 90.. 5 phenyl hydrazine... 21.0 15.0 6.0 4.0 91.. 1 phenyl hydrazine... 7.5 2.7 92.. 3.6 hydrazine 13.8 8.4 4.2 2.5 93.. 1 hydrazine 12.3 8.1 6.9 94.. 0.5 hydrazine 17.4 13.8 12.6 95. 2 hydrogen peroxide... 21.6 20.4 17.4 15.0 96.. 1 hydrogen peroxide... 20.1 18.9 17.7 97. 5 sodium perborate..... 20.4 18.9 17.4 98.. 1 sodium perborate.. 20.1 19.2 18.3 99.... 5 calcium hypochlori 6.9 2.4 100. 1' calcium hypochlorite 10.2 3.9

Reference to Example 8 shows that carboxymethylthat 30 pounds of hydroxyethyl cellulose was used as hydroxyethyl cellulose, which is an excellent thickening agent for aqueous liquids, can be made to degrade autogeneously and the aqueous liquid containing it can be therefore desirably lowered in viscosity by admixwas also admixed the various viscosity reducers accordwre therewith of a viscosity reducing agent according ing to the invention Viscosities were obtained at 80F.

to the The initial viscosity was 40.8 centipoises. The salient facts and results are set out in Table VI, infra.

30 the polymer per 100 gallons of water to increase the viscosity of the resulting aqueous solution with which EXAMPLE 9 This series of tests was similar to those above except TABLE Vl.-DEGRADAT1ON OF HYDROXYETHYl. CELLULOSE USING OXlDlZERS AND AMlNE AGENTS AT VARIED I TEMPERATURE AND CONCENTRATION VALUES TEsT APPARATUS: FAN VISCOSIMETER PROCEDURE: T ELDBQKYETEYLLELEULOSE WAVSAADDED TO THE WATER AND AGITATED wITH A PALO sTIRRER UNTIL FULLY HYDRATED. THE VlSCOSlTY REDUcER wAs ADDED AND AGITATED UNTIL DIss0LvED OR DISPERSED. THE VlSCOSlTY wAs MEASURED PRIoR To ADDING THE vIscsoITY REDUCER AND PERIODICALLY THEREAFTER.

- Polymer in Ratio of pounds per polymer Temper- I Viscosity in cps after -Test 1000 to addiature identification gallons Additive in lb/1000 gallons tive in F 1 hr 4 hrs 24 hrs 48 hrs 30 None 80 39.5 39 5 40.0 39 9 3p Ammonium persulfate. 0.25.. 80 30.0 18 0 4 5 2 4 30 Phenylhydrazine, 0.25 120 80 4.2

30 Phenylhydrazine, 0.1.. 300 13.8 12.0 8.4 8.0

30 Phenylhydrazine, 0.05 600 80 20.1 18.6 13.4 13.0

30 Potassium periodate, 1.0 30 80 32.4 32.1 29.4 28.0

30 Potassium periodate, 0.2 120 80 34.8 35.4 33.0 32.0

None 234.0

70 Phenylhydrazine, 0.1.; 700 80 222.0 216.0

70 Potassium periodate, 2.. 35 80 190.0 180.0

70 Potassium periodate, 0.25. 280 80 225.0 192.0

30 None 125 23.5 22.8 21.0

30 Phenylhydrazine, 0.1..... 300 125 3 3 30 Potassium periodate, 0.25. 120 125 14 4 14.1 13.5 12 0 70 None 125 158 149 140 148 70 Calcium hypochlorite, 5. 14 125 52 6.0

70 Calcium hypochlorite, 1. 70 125 120 63 60 70 Hydrazine sulfate, 1 70 125 142 126 20 4 9.6

70 Hydrazine sulfate, 0.25.. 280 125 154 141 123 117 70 Potassium pen'odate. 70 125 148 126 105 70 Potassium periodate, 0.25. 280 125 152 135 126 70 Potassium periodate, 2.0... 35 109 84 6 82 2 80 70 Phenylhydrazine,0.1 ..II 700 12s 10s 9514 5710 48.6

Reference to Table VI of Example 9 shows that the practice of the invention, employing the viscosity reducing agent required, results in a sufficiently low viscosity within a relatively short time to permit easy removal of the hydroxyethyl cellulose polymer composition from its emplaced location, as for example, from a geologic formation.

EXAMPLE 10 The procedure of the above Example 9 was repeated employing various polymers, in the amount of 30 pounds per 1,000 gallons of a solution consisting of 80 percent water and 20 percent isopropyl alcohol (by volume) and employing various viscosity reducers in different amounts, according to the invention, at a temperature of 80F. The significant facts and viscosity val- 1168 ned l91 Table. vlla n raatm;

18 A polymer plugging composition wasprepared by admixing (a) a premix. of 90 percent guar gum, 8% Nal-l- CO and 2 percent polyacrylamide with water. in an amount sufficient to provide 500 pounds thereof per 1,000 gallons of resulting composition and (b) 15 pounds of sodium dichromate and (c) 2 pounds of po- TABLE Vll.EFFlCACY OF VARIOUS VISCOSITY REDUCING AGENTS ON 80% WATER-20% ALCOHOL DISPERSIONS OF VARIOUS POLYMERS AT 80F Farm viscosity in cps after Test Polymer and concentrate in identification lb/1000 gallons Additive in lb/1000 gallons 1 hr 2 hrs 4 hrs 24 hrs 48 hrs hydroxyethyl cellulose None 47.4 48.6 49.2 52.8 30 hydroxyethyl cellulose... Phenylhydrazine, 5.. 45.0 42.0 46.8 27.0 30 hydroxyethyl cellulose... Hydrazine sulfate, 5 49.2 49.8 51.0 55.8 30 hydroxyethyl cellulose... Hydroxylamine hydrochloride, 5.. I 50.4 51.0 52.2 54.6 30 hydroxyethyl cellulose... Ammonium persulfate, 5 50.4 49.2 46.8 39.0 30 hydroxyethyl cellulose... Potassium perrnangate, 5 42.0 34.2 30.0 24.0 30 hydroxyethyl cellulose Potassium periodate, 5... 48.6 40.8 21.8 3.0 p 30 polyacrylamide made by pro None. 66.3 66.6 66.0 65.0

cedure B. 127 30 polyacrylamide made by pro- Hydrazine, 5 66.9 66.9 65.0. 63.0 cedure B.

128 30 polyacrylamide made by pro- Hydrazine, 5 ppm FeCl 60.0 61.8 61.2

cedure B. 129 30 polyacrylamide made by pro- Phenylhydrazine, 5 64.8 63.6 57.6 57.6

cedure B. 130 30 polyacrylamide made by pro Hydrazine sulfate, 5 55.8 56.4 53.4 53.4

. cedure B. 131 30 polyacrylamide made by pro Hydrazine sulfate, 5 +50 ppm 44.4 36.6 30.6

I cedure B. FeCl- 132 30 polyacrylamide made by pro- Hydrazine sulfate, 5 50 ppm 43.2 32.4 26.4 cedure B. I FeCI 133 30 polyacrylamide made by pro- Hydroxylamine hydrochloride, 5 55.2 55.8 35.4

cedure B. 134 30 polyacrylamide made by pro- Hydroxylamine hydrochloride, 18.0 10.8 6.0 cedure B. 5 +50 ppm FeCl 135 30 polyacrylamide'made by pro- 50 ppm FeCl 60.0 61.8 61.2

cedure B. 136 30 polyacrylamide made by pro- 50 ppm FeCl u' 57.6 61.8 61.8 cedure B. Y 137 30 polyacrylamide made by pro- Potassium periodate, 5 66.9 65.5 65.0

cedure B. q 30 carboxymethylhydroxyethyl None 30.0 33.0 31.2 33.0

- cellulose. 138 30 carboxymethylhydroxyethyl Potassium periodate, 31.2 31.8 17.1 7.8

cellulose. 139 30 carboxymethylhydroxyethyl Potassium periodate, 1 30.3v 32.7 28.5 27.0

cellulose.

1 Initial viscosity of 30 pounds of hydroxyethyl cellulose per 1000 gallons of water was 48 cps.

Initial viscosity of 30 pounds of polyacrylamide made by procedure A was 66.6 cps.

Reference to Table VI] shows that solutions of water EXAMPLE 1 l A temporary plug was inserted and degraded in accordance with the inyention as follows:

ment of a geologic formation traversed by a well as a diverting agent for injected fluid, had been known to resist removal thereafter and interfere with fluid flow in the formation. In this example, no problem of that nature could occur.

EXAMPLE 12 in this example the use of adipic anhydrazide (l) and sebacic dihydrazide (11) as breakers for polyacrylamide (PA) (molecular weight of between about 2 and 3 million) and hydroxyethyl cellulose (HEC) thickened q $911 i mi us r A t e tai th fol lowing Table'Vlll shows both breakers are effective in breaking the thickened solutions. As noted hereinbefore some breakers are more effective'in breaking with certain polymers, i.e. at 80F both breakers more effecified starches to increase the viscosity from about 10 to about 5,000 centipoise, measured at a temtively broke the HEC than the PA solution. But at 5 perature of about 25C with a Fann viscometer t higher temperatures (125F) the breakers were more 100 rpm, and incorporating in said aqueous solueffective in breaking the PA solution. tion a sufficient amount of a breaker which when TABLE vlll Viscosity (cps) Gelling agent and cone. Breaker and cone. Temp. (lbs/I000 gal.) (lbs/I000 gals.) F Initial 1 hr 18 hrs 23 hrs 72 hrs PA 30 lbs None 80 48.0 51.0 51.0 48.0 46.2 PA 30 lbs 15 lbs.. 80 48.0 51.0 48.0 40.8 36.6 PA 30 lbs... 1 5 lbs.. 125 40.8 42.0 24.0 22.2 6.0 PA 30 lbs...... II 5 lbs... 8Q 48.0 51.0 48.0 40.8 36 PA 30 lbs ll lbs... 125 40.8 42.6 30.0 26.8 12.0 PA 30 lbs None 125 40.8 42.0 42.0 41.0 36.0 HEC 30 lbs None... 80 42.0 42.0 42.0 39.0 32.4 BBC 30 lbs lbs.. 80 42.0 39.6 24.0 16.2 5.2 HEC lbs 15 lbs.. 125 22.0 25.0 3.0 2.4 HEC 30 lbs None 125 22.0 22.0 18.0 14.4 HEC 30 lbs l1 5 lbs... 80. 42.0 39.0 22.2 13.6 4.2 HEC 30 lbs II 5 lbs 125 22.0 14.4 3.4 l.8

v The invention has utility in any instance where a temdispersed in said aqueous solution disassociates to porary plugging or lessening or inhibition of fluid flow 5 form hydrazinium ions selected from the group is desirable, e.g. in hydraulic fracturing (where the consisting of a water soluble hydroxylamine compolymer is desirable to aid in suspendmg a proppant) pound, a water soluble hydrazine compound or a and in cementing a subterranean formation wherein i t h f, to decrease h viscosity f h p 'y fluld comm] devised and during dfllthickened aqueous solution, prior to removing said ling to shut off water lntruslon, thereby not perma- 30 aqueous Solution f the formation nently lessening the permeability of the fonnation after 2 The method f i 1 wherein the organic wfollowing a short period during which the polymer emis p0|yacry]amide P y degrades- 3. The method of claim 1 wherein the organic polylt wlll be apparent to those knowledgeable of the nais a cellulose ethen ture and properties of water dispersible polymers that The method of claim 1 wherein the breaker is other such polymers than those employed in the examdrazine Sulfate or phenyl hydrazine ples hereof can be used, including any one or combina- The method of claim 4 wherein the polymer is tion of those named herein. Similarly, other amines of polyacrylamide the nature of those used in the examples, and other per- The method of claim 4 wherein the polymer is a oxldes of the nature of those used 1n the examples can cellulose ether be used as the viscoslty reducer 1n the practice of the 7. The method of Claim 1 wherein the breaker is m l droxylamine hydrochloride.

at c me 8. The method of claim 7 wherein the polymer is l. in a method of treating a subterranean formation polyacrylamide 5 pnetrated b a wellbre,wherem W Solunon 9. The method of dam 7 whereln the polymer 1s a thlckened with a polymeric materlal 1s ln ected through cellulose ether sald borehole andunto contact w th the formatlon, 1s The method of claim 1 wherein the polymer is permftted 9 remam Contact wlth the formanon for carboxymethyl hydroxyalkyl cellulose ether and the penof 9 and remove d from the forma' breaker is selected from the group consisting of hytlon'the {PW whlch FomPnsesi droxylamine hydrochloride, hydrazine, hydrazine sulthickenlng said aqueous fluid wlth a sufiiclent quanf or pheny] hydrazine tity of a polymeric additament selected from the group consisting of acrylamide polymers and co- 522 33 UNITED STATES PATENT OFFICE QERTIFIQATE OE @ORQRECTIOTN Patent 1 Dated June 25, 1974 Invent r( K0 H- .Nimerick It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

The title should, read M THOD OF TREATING SUBTERRANEAN FORMATIONS WITH A COMPOSITION OF IMPROVED VISCOSITY CONTROL.

In column 1, line-29, delete "having" and insert -varying-.

In column 3, lin 66, 2nd column, delete before Pd and insert In column 12, line 2, delete "of before l50F and insert et In column 12, Table II, in column titled 48 hrs, lst item, delete "38.0" and insert --36,0-=--.

In column 14, Table IV, in column titled 48 hrs, 15th item, delete "16.1" and insert --l6.6-.

In column 16, line 1, delete "carbomethyl" and insert --carboxymethyl--,

In column 16, line 30, delete "100" and-insert l000--'.

In column 16, Table VI, in heading titled procedure, 3rd line, delete 'viscsoity and insert --viscosity-..

In column 16., Table VI, in column titled Temp in F, 4th item, delete "60" and insert --80-.

In. column 17, Table VII, footnote 1, line 1, after "cellulose" add -=-polymer.

In column 18, line-l2, delete "diverging" and insert -diverting--.

;In column 20, Table VIII, in column titled 72 hrs, 8th item,

delete "5.2" and insert --4.2--.

Signed and sealed this 5th day of November 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. C Attesting Officer MARSHALL DANN Commissioner of Patents 

2. The method of claim 1 wherein the organic polymer is polyacrylamide.
 3. The method of claim 1 wherein the organic polymer is a cellulose ether.
 4. The method of claim 1 wherein the breaker is hydrazine sulfate or phenyl hydrazine.
 5. The method of claim 4 wherein the polymer is polyacrylamide.
 6. The method of claim 4 wherein the polymer is a cellulose ether.
 7. The method of claim 1 wherein the breaker is hydroxylamine hydrochloride.
 8. The method of claim 7 wherein the polymer is polyacrylamide.
 9. The method of claim 7 wherein the polymer is a cellulose ether.
 10. The method of claim 1 wherein the polymer is carboxymethyl hydroxyalkyl cellulose ether and the breaker is selected from the group consisting of hydroxylamine hydrochloride, hydrazine, hydrazine sulfate or phenyl hydrazine. 